Adult periodontitis is a biota shift disease caused by an ecological transition of the dental plaque, and consequent chronic inflammation. Understanding the physiology of dental plaque and its complex ecology, to the point where it can be controlled, is therefore central to the prevention and treatment of periodontal disease. Dental plaque is an ecologically complex biofilm with over 350 microbial taxa represented; however the organization of the biofilm is not random. Oral streptococci, including Streptococcus gordonii, are among the first bacteria to colonize the pellicle coated tooth surface, creating a template for the subsequent attachment of other bacterial species, ultimately including periodontal pathogens. The initial binding of the tooth surface by pioneer species, such as S. gordonii, is therefore pivotal in the establishment of ecological communities associated both with gingival health and disease. The central hypothesis of this proposal is that within the dental plaque biofilm, bacteria are sentient and contribute to its maintenance, physiology, and development through receipt, transmission and response to chemical and physical signals. The goals of the proposed study are therefore to develop and use an optimized differential display approach, and scanning laser confocal microscopy, to: 1) identify the critical communications between bacteria that regulate growth and microcolony formation in a model biofilm, 2) identify bacterial responses to environmental cues, which include signals derived from other bacterial species as well as the host, and 3) determine the effect of biofilm formation on an additional form of intercellular communication, genetic exchange. The practical benefit of this study is that it may lead to new strategies for subverting or regulating key interactions in oral biofilm formation, and therefore to new therapies for controlling its establishment, rendering it sensitive to antibiotics, and facilitating its removal.